Electrochemical processes can remove oxygen from air by ionizing oxygen molecules on one surface of an electrolyte and then transporting the oxygen ions through a solid electrolyte. The oxygen molecules are then reformed on an opposite electrolyte surface. An electric potential is applied to a suitable catalyzing electrode coating applied to the surface of the electrolyte. The electrode coating is porous to oxygen molecules and acts to dissociate oxygen molecules into oxygen ions at its interface with the electrolyte. The oxygen ions are transported through the electrolyte to the opposite surface, which is also coated with a catalyzing electrode and electrically charged with the opposite electric potential which removes the excess electrons from the oxygen ions, and the oxygen molecules are reformed.
Although electrochemical devices are generally known there are significant disadvantages associated with using known devices as oxygen generators. For example, in the fuel cells described in U.S. Pat. Nos. 4,640,875 and 5,306,574, the individual electrodes are made from a ceramic material while the manifold into which each of the electrodes is inserted is made from stainless steel. This structure is difficult and expensive to manufacture because many parts must be assembled. More importantly, the electrochemical device operates at high temperatures, typically between 700-1000.degree. C., and the different coefficients of thermal expansion between the stainless steel and the ceramic frequently cause cracks and thus leakage between the ceramic electrode and the stainless steel manifold. This leakage can be especially severe if a high pressure is developed within the electrochemical device. For example, oxygen generators capable of producing at oxygen at high pressures of 2000 psi are unknown to the inventors.
Further in both of these electrochemical devices, whether the device is used as an oxygen generator or as a fuel cell, the electrical interconnections used to form a series-parallel array between the electrodes require direct contact of the outer peripheries of the individual electrodes. The interconnection arrangement is expensive to manufacture, less reliable in operation, and reduces the surface area available for electrochemical exchange.
It is, therefore, an object of the present invention to provide a ceramic electrolyte element which can be formed and used in an electrochemical device.
It is another object of the invention to provide a ceramic electrolyte element having a configuration which provides for an increased active surface area per unit volume and weight of ceramic material.
It is yet a further object of the invention to provide a composition including an electrolyte and a binder which can be injection molded to form a ceramic electrolyte element.
Another object of this invention is to provide a ceramic electrochemical device wherein the electrical connections connecting the electrodes are simplified.
A further object of this invention is to provide an electrochemical device capable of delivering oxygen at 2000 psi or greater.
Still another object of this invention is to provide a ceramic electrochemical device which is of a modular configuration and thereby provides a simple "building block" approach to meet differing requirements for amounts of oxygen to be generated.